Some igneous rock forms from magma that cools slowly within Earth’s crust. Briefly describe the most likely crystallization and texture of the rock. Other igneous rock forms from lava that cools quickly on Earth’s surface. Classify the rock as either intrusive or extrusive, and identify another word used to describe this type of rock. You are studying a sample of igneous rock. The rock formed on the surface of Earth. It’s made mostly of light-colored minerals. The sample has just a few specks of dark-colored minerals. Classify the rock by type and composition. You are studying a sample of igneous rock. The rock formed within Earth’s crust. The sample contains a very high concentration of dark-colored, high-density minerals. Classify the rock by type and composition. A scientist shows you a sample of rock called gabbro. The scientist explains that gabbro is an intrusive mafic igneous rock. Explain what this means.